1. Field of the Invention
This invention relates to electromachining and electropolishing of metals and the like and more particularly to sequential electromachining and electropolishing by changing the conditions of the electrolytic process.
2. Brief Description of the Prior Art
It is often desirable or necessary to provide for the manufacture of metal articles with a smooth polished surface. Conventional manufacturing operations, however, e.g., cutting, turning, forging, casting, drilling, and the like, often leave an object with finished shape and dimensions, but a surface that is marred by machine marks or tool lines, burrs, flashings, and the like. Consequently, the manufactured article must be subjected to a final finishing step of removing burrs and similar relatively large defects and a final polishing step that provides a very smooth, even mirrorlike, surface. Removal of burrs and relatively large imperfections has often been performed by hand, with resultant large expenditure of time and effort. Small parts have been polished by tumbling with abrasive powders. Chemical-mechanical polishing has also been used. Flat surfaces, in particular, have also been finished by electropolishing, wherein a smooth electrode is positioned very close to the surface and an electric current is passed between the electrode, as cathode, and substrate surface, as anode, in order to remove small roughnesses on the substrate.
More recently, it has been discovered that electrochemical deburring can be conducted using charge-modulated electrochemical dissolution. Such a process is disclosed in copending U.S. patent application Ser. No. 09/080,264, now U.S. Pat. No. 6,402,931 the entire disclosure of which is incorporated herein by reference. However, it as been found that charge modulated conditions that are appropriate for deburring are not always suitable for electropolishing.
Accordingly, a need has continued to exist for a method of conducting electrochemical smoothing of machined surfaces that can provide a finished polished surface.
The problem of providing a finished polished surface by an electrochemical procedure applied to the surface of a manufactured article has now been alleviated by the method of this invention. According to the invention a surface of an electrolytically dissolvable material, e.g., an electrolytically dissolvable metal, can be smoothed by a two-step electrochemical process wherein a surface to be smoothed and a counterelectrode are contacted with an electrolyte and an electric current is passed between the substrate and counterelectrode, wherein the substrate is predominantly anodic with respect the counterelectrode. In a first step the electrolytic environment at the substrate surface is maintained as a macroprofile until the relatively large roughness has been eliminated, and, in a second step, the electrolytic environment at the substrate surface is maintained as a microprofile to complete the electropolishing of the surface.
Accordingly, it is an object of the invention to provide a method for smoothing the surface of a manufactured article.
A further object is to provide a method for electrochemically deburring and polishing a metal surface.
A further object is to provide a method for deburring and polishing a metal surface using charge-modulated electrodissolution.
A further object is to provide a method for electrolytically smoothing a metal surface by using charge-modulated electrochemical dissolution wherein relatively large asperities are removed using a first pulsed current waveform and small asperities are removed using a second pulsed current waveform.
A further object is to provide a method for smoothing a metal surface using charge-modulated electrochemical dissolution wherein relatively large asperities are removed by maintaining the electrochemical environment at the surface in a macroprofile regime and the small asperities are removed by maintaining the electrochemical environment at the surface in a microprofile regime.
Further objects of the invention will be apparent from the description of the invention that follows.